<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        // [] {} if([]) if({})都是真  if（null） if(NaN)假的
        if (null) {
            console.log('aaa1111');
        }
        for (var i = 0; i < 10; i++) {
            var a = 100
            console.log('aaa');

        }
        console.log(a);
        console.log(i);

        var score = 97
        function getScore(score) {
            if (score > 90) {
                return alert('优秀')
            }
            if (score > 60) {
                return alert('及格')
            }
            return alert('不及格')


        }
        getScore(score)
        switch (key) {
            case 0:
                console.log('a');
                break
            case 1:
                console.log('b');
        }
    </script>
</body>

</html>